Benzodiazepine Toxicity

Etiology

Leo Sternbach was an Austrian scientist working for Hoffmann-La Roche in Nutley, NJ, and has been accredited for his work in developing many drugs, in particular, benzodiazepines. In 1956, he serendipitously created chlordiazepoxide, which was approved for medical use in 1960. He later developed an improved, safer version named diazepam in 1963. Diazepam became widely popular, and between 1969 and 1982, it was the most prescribed drug in the United States, with over 2.3 billion doses sold in its peak year in 1978.[4]

Epidemiology

While precise data is unavailable, estimates suggest a lifetime prevalence of benzodiazepine use disorder to be less than 1%. Benzodiazepines, though, are often combined with other drugs. Thus the prevalence of an isolated benzodiazepine use disorder is difficult to determine from epidemiologic studies. Existing data suggest that the lifetime prevalence of tranquilizer and sedative use, which includes benzodiazepines and barbiturates in the United States, are around 1% and 1.1%, respectively. In 2013, 2% of the United States population (12 years or older) had consumed benzodiazepines or barbiturates for nonmedical use. From 1996 to 2013, benzodiazepine prescriptions increased by 2.5% each year, making it one of the most prescribed medications in the world. Substance abuse disorder treatment centers reported admissions for benzodiazepine abuse as the sole primary substance or drug of choice to have increased by 109% between 2003 and 2013.

Pathophysiology

Benzodiazepines are organic bases with a benzene ring and a 7-member diazepine moiety, with variable side chains that determine the potency, duration of action, metabolite activity, and rate of elimination. Benzodiazepines exert their effect via modulation of the gamma-aminobutyric acid A (GABA-A) receptor, the primary inhibitory neurotransmitter in the central nervous system. The GABA-A receptor, depending on various arrangements of its subunits, determines its affinity for various agents that bind to the receptor. Benzodiazepines bind at the interface of the GABA-A receptor and subsequently lock the receptor into a configuration that increases its affinity for GABA. Benzodiazepines do not alter the production, release, or metabolism of GABA but instead potentiates its inhibitory actions by augmenting or enhancing receptor binding. This binding ultimately increases the flow of chloride ions through the GABA ion channel, causing postsynaptic hyperpolarization, which decreases the ability to generate an action potential. The low incidence of respiratory depression with benzodiazepines, which differentiates it from barbiturates, is related to the low density of binding sites in the brainstem, which houses the respiratory center.[5]

Toxicokinetics

Benzodiazepines taken in toxic doses without other coingestants rarely cause a significant toxidrome. The classic presentation in patients with isolated benzodiazepine overdose will include central nervous system (CNS) depression with normal or near-normal vital signs. Many patients will still be arousable and even provide a reliable history. Classic symptoms include slurred speech, ataxia, and altered mental status. Respiratory compromise is uncommon in isolated benzodiazepine ingestions, but if taken with coingestants such as ethanol or other drugs/medications, respiratory depression can be noted. It is important to note that most intentional ingestions of benzodiazepines do involve coingestants, the most common being ethanol, leading to substantial respiratory depression and airway compromise. The dose required to produce respiratory compromise is difficult to quantify and depends on multiple factors, including dosage, tolerance, weight, age, coingestants, and even genetics. Patients with severe toxicity will present in a stuporous or comatose state, and immediate airway management and mechanical ventilation may be required.

A unique toxidrome related to parenteral formulations of diazepam and lorazepam is propylene glycol poisoning. Propylene glycol is the diluent used in the parenteral formulations for these two benzodiazepines, and prolonged use can cause propylene glycol toxicity, which includes skin and soft tissue necrosis, hemolysis, cardiac dysrhythmias, hypotension, significant lactic acidosis, seizure, and multisystem organ failure. While propylene glycol toxicity is rare, it must be considered when patients are receiving large or continuous infusions of parenteral benzodiazepines, for example, when treating severe sedative or ethanol withdrawal syndromes such as delirium tremens.

History and Physical

Patients with benzodiazepine toxicity will primarily present with central nervous system depression ranging from mild drowsiness to a coma-like, stuporous state. The classic presentation of an isolated benzodiazepine overdose consists of CNS depression with normal vital signs. Cardiac-related effects and fatalities are rare in pure benzodiazepine toxicities. Respiratory depression or compromise, while less common when compared to barbiturates, is the most important adverse effect requiring immediate intervention. Life-threatening respiratory depression can be seen with large oral ingestions with or without coingestants. Iatrogenic causes of toxicity can be seen when benzodiazepines are combined with other drugs during procedural sedation, particularly with opiates such as fentanyl.

In children with benzodiazepine toxicity, most will have symptoms within four hours of ingestion. Ataxia is the most common sign of toxicity in children, occurring in 90% of pediatric patients. Respiratory compromise occurs in less than 10% of pediatric cases, and hypotension has not been reported.

Evaluation

Benzodiazepine overdose is usually suspected or diagnosed based on clinical presentation. Many patients are arousable and can provide supporting information regarding their ingestion. In the acutely poisoned patient who cannot provide an adequate history, a general approach should be undertaken to stabilize the patient.[6]

Before any diagnostic tests are ordered in the patient presenting with altered mental status with suspected overdose or toxicity, any respiratory or abnormal vital signs should be addressed first. Mechanical ventilation may be required to address respiratory compromise and intravenous fluids administered to manage hemodynamic instability.

In terms of general diagnostic testing, routine testing for the acutely poisoned patient should include a point of care glucose to immediately rule out and address hypoglycemia as the cause of altered mental status. Acetaminophen and aspirin levels, along with ethanol levels, should be ordered to evaluate for possible coingestions. An ECG should be ordered to rule out the ingestion of drugs that may widen the QRS or QTc intervals and may precipitate arrhythmias. A pregnancy test should be ordered for all women of childbearing age. A head CT without contrast may be considered to rule out an intracranial abnormality related to the patient presenting with an acutely altered mental status.

While a standard urine drug screen (UDS) should be ordered, it comes with many limitations. Qualitative immunoassays for benzodiazepines in urine are readily available but do not typically aid in acute management decisions. Most of these screening tests detect only benzodiazepines that are metabolized to oxazepam glucuronide. Some benzodiazepines such as clonazepam, lorazepam, midazolam, and alprazolam will not show up on many urine drug screens as a result. A positive urine drug screen only indicates recent exposure but does not confirm causality for acute toxicity or overdose, nor does it name a specific agent.

Treatment / Management

The mainstay treatment for acute benzodiazepine toxicity is supportive care, which may include endotracheal intubation to provide definitive airway management. Single-dose or multi-dose activated charcoal, hemodialysis, or whole bowel irrigation play no role in managing benzodiazepine toxicity.

While the mainstay treatment of acute benzodiazepine toxicity or overdose is supportive care, there is, however, an “antidote” that may be used in limited situations. Flumazenil is a nonspecific competitive antagonist at the benzodiazepine receptor that can reverse benzodiazepine-induced sedation. However, in most cases, the risks of flumazenil usually outweigh the benefits in acute toxicity, and thus flumazenil is not recommended for routine reversal of this sedative agent. Seizures and cardiac dysrhythmias, particularly PSVT, can occur after flumazenil administration, and many fatalities have been reported. Flumazenil can precipitate acute withdrawal syndromes in those with chronic benzodiazepine dependence, which can be life-threatening. If a patient with a chronic dependence on benzodiazepines is given flumazenil, it can lower their seizure threshold and potentially cause life-threatening seizures. The treatment of seizures, which typically involves benzodiazepines, would be rendered useless, as the flumazenil has blocked the benzodiazepine receptors.

Flumazenil can be safely administered to non-habituated users of benzodiazepines. This situation classically occurs in the pediatric population with accidental ingestion or after procedural sedation. It is recommended that the decision to use flumazenil be based on the balance of risk versus benefit in the assessment and treatment of a patient that is a non-habituated user of benzodiazepines, as most people with a benzodiazepine overdose will do well with supportive care and time alone.[7][8][9](B3)

Differential Diagnosis

The differential diagnosis of benzodiazepine toxicity includes:

• Alcohol toxicity
• Hypoglycemia
• Hyponatremia or hypernatremia
• Stroke
• Opiate toxicity

Prognosis

The prognosis depends on how quickly the diagnosis is made and the treatment administered.

Complications

The complications of benzodiazepine toxicity include:

• Respiratory arrest
• Death
• Aspiration pneumonitis
• Rhabdomyolysis